Currently, a conventional ionization chamber is not able to detect real-time temperature inside the cavity of the ionization chamber; as such radiation dose measurement can only be performed after the temperatures inside and outside the cavity of ionization chamber had reached a thermal equilibrium. Thus, not only there will be a great amount of time being wasted for the waiting of thermal equilibrium, but also certain errors in a radiation dose measurement signal correction are inevitable since the signal correction is performed based upon an assumed temperature inside the cavity which is actually the temperature detected outside the cavity
Please refer to FIG. 1, which is a cross sectional view of a conventional ionization chamber. As shown in FIG. 1, the cavity 10 is an area producing ionization signals and is formed from the enclosure of the chamber wall 11 and is isolated from external environment, whereas the electrode 12 is provided for collecting ionization signals. It is noted that when the chamber wall 11 is made of a conductive material, the chamber wall 11 itself can be used as an outer electrode 13, but when the chamber wall 11 is made of an insulating material, there will be a conductive material to be coated on the inner surface of the chamber wall 11 so as to form an outer electrode 13. Moreover, the inner electrode 12 is insulated from a guard electrode 14 by an insulating material or air, whereas the chamber stem 15 is provided for fixing the ionization chamber. When in connection, signals detected by the inner electrode 12 are being transmitted via the signal line 121, and the electrical potentials of the guard electrode 14 and the inner electrode 12 are maintained at the same level while applying a high voltage between the inner electrode 12 and the outer electrode 13. Generally, there are small ventilation holes formed on the chamber wall 11 of a conventional ionization chamber for allowing air to flow in and out the ionization chamber. Nevertheless, the conventional ionization chambers still suffer the following shortcomings:                (1) Since there is no way to measure real-time temperature inside the cavity 10 of a conventional ionization chamber, usually a temperature detected by a thermometer 16 that is disposed outside the cavity 10 is used as the real-time temperature inside the cavity 10. Thereby, the actual temperature variation happening inside the cavity 10 may not be reflected in real time on the change of temperature outside the cavity 10 through the air communication via ventilation holes. Consequently, there can be errors being caused in the correction process of radiation dose measurement signals.        (2) The radiation dose measurement of a conventional ionization chamber can only be performed after the temperatures inside and outside the cavity 10 of the ionization chamber had reached a thermal equilibrium, whereas the waiting period can be hours or even longer than a day, depending on the size of the cavity 10.        
Therefore, it is in need of an improved ionization chamber capable of effectively improving the accuracy of measurement and greatly reducing the time spent in radiation dose measurement.